5. ECO-WORTHY 12 Volts 5 Watts Portable Power Solar Panel Battery Charger Backup for Car Boat Batteries(Click Link to Check Price on Amazon)Editor’s Rating : 8.8 out of 10Perfect trickle charger/maintainer for 12V batteries of cars, motorcycles, boats, snowmobiles, tractors etc.Please note that the protective plastic film on the panel surface is supposed to peel off. The cigarette plug option only works if it has constant power when the key is out of the ignition. When you start the car, please remove the solar panel from the car battery.